Field device in a process control system using wireless radio communications to transmit and receive sense and control signals

ABSTRACT

An apparatus provides wireless communication between multiple devices within a process control system, such as between field devices, control units, user terminals, controllers, etc., using a wireless bus protocol. In one embodiment, a process control system for use within a process control environment includes a plurality of process control field devices that operate within the process environment, and a control device adapted to receive a sense signal from or to provide a control signal to one or more of the plurality of process control field devices. First and second wireless transceivers are communicatively connected to different ones of the process control field devices and the control device and communicate with one another using a bus protocol, to thereby provide wireless communications within the process control system.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of pending U.S. application Ser. No.09/805,124, filed Mar. 8, 2001 and entitled “Apparatus for ProvidingRedundant Wireless Access to Field Devices in a Distributed ControlSystem” (which is hereby expressly incorporated by reference herein);

-   -   which is a Continuation of U.S. application Ser. No. 08/864,750,        filed May 28, 1997, entitled “Distributed Control System for        Controlling Material Flow Having Wireless Transceiver Connected        to Industrial Process Control Field Device to Provide Redundant        Wireless Access”, which issued as U.S. Pat. No. 6,236,334 on May        22, 2001;    -   which is a Continuation of U.S. application Ser. No. 08/782,513,        filed Jan. 9, 1997, entitled “Distributed Control System Having        Central Control Providing Operating Power to Wireless        Transceiver Connected to Industrial Process Control Field Device        Which Providing Redundant Wireless Access”, which issued as U.S.        Pat. No. 5,682,476 on Oct. 28, 1997;    -   which is a Continuation of U.S. application Ser. No. 08/483,119,        filed Jun. 7, 1995, and entitled “An Apparatus for Providing        Redundant Wireless Access to Field Devices in a Distributed        Control System”, now abandoned;    -   which is a Continuation-in-Part of U.S. application Ser. No.        08/328,324, filed Oct. 24, 1994 and entitled “An Apparatus for        Providing Non-Redundant Secondary Access to Field Devices in a        Distributed Control System”, now abandoned.

BACKGROUND

This invention relates to accessing field devices in a distributedcontrol system. Specifically, this invention relates to providingredundant wireless access to such field devices remotely using wirelesstransceivers.

In a typical industrial plant, a distributed control system (DCS) isused to control many of the industrial processes performed at the plant.Typically, the plant has a centralized control room having a computersystem with user I/O, disc I/O, and other peripherals as are known inthe computing art. Coupled to the computing system is a controller and aprocess I/O subsystem.

The process I/O subsystem includes a plurality of I/O ports which areconnected to various field devices throughout the plant. Field devicesknown in the control art include various types of analytical equipment,silicon pressure sensors, capacitive pressure sensors, resistivetemperature detectors, thermocouples, strain gauges, limit switches,on/off switches, flow transmitters, pressure transmitters, capacitancelevel switches, weigh scales, transducers, valve positioners, valvecontrollers, actuators, solenoids, and indicator lights. As used herein,the term “field device” encompasses these devices, as well as any otherdevice that performs a function in a distributed control system and isknown in the control art.

Traditionally, analog field devices have been connected to the controlroom by two-wire twisted pair current loops, with each device connectedto the control room by a single two-wire twisted pair. Analog fielddevices are capable of responding to or transmitting an electricalsignal within a specified range. In a typical configuration, it iscommon to have a voltage differential of approximately 20-25 voltsbetween the two wires of the pair and a current of 4-20 milliampsrunning through the loop. An analog field device that transmits a signalto the control room modulates the current running through the currentloop, with the current proportional to the sensed process variable. Onthe other hand, an analog field device that performs an action undercontrol of the control room is controlled by the magnitude of thecurrent through the loop, which is modulated by the I/O port of theprocess I/O system, which in turn is controlled by the controller.Traditional two-wire analog devices having active electronics can alsoreceive up to 40 milliwatts of power from the loop. Analog field devicesrequiring more power are typically connected to the control room usingfour wires, with two of the wires delivering power to the device. Suchdevices are known in the art as four-wire devices and are not powerlimited, as are two-wire devices.

In contrast, traditional discrete field devices transmit or respond to abinary signal. Typically, discrete field devices operate with a 24 voltsignal (either AC or DC), a 110 or 240 volt AC signal, or a 5 volt DCsignal. Of course, a discrete device may be designed to operate inaccordance with any electrical specification required by a particularcontrol environment. A discrete input field device is simply a switchwhich either makes or breaks the connection to the control room, while adiscrete output field device will take an action based on the presenceor absence of a signal from the control room.

Historically, most traditional field devices have had either a singleinput or a single output that was directly related to the primaryfunction performed by the field device. For example, the only functionimplemented by a traditional analog resistive temperature sensor is totransmit a temperature by modulating the current flowing through thetwo-wire twisted pair, while the only function implemented by atraditional analog valve positioner is to position a valve between anopen and closed position, inclusive, based on the magnitude of thecurrent flowing through the two-wire twisted pair.

More recently, hybrid systems that superimpose digital data on thecurrent loop have been used in distributed control systems. One hybridsystem is known in the control art as the Highway Addressable RemoteTransducer (HART) and is similar to the Bell 202 modem specification.The HART system uses the magnitude of the current in the current loop tosense a process variable (as in the traditional system), but alsosuperimposes a digital carrier signal upon the current loop signal. Thecarrier signal is relatively slow, and can provide updates of asecondary process variable at a rate of approximately 2-3 updates persecond. Generally, the digital carrier signal is used to send secondaryand diagnostic information and is not used to realize the primarycontrol function of the field device. Examples of information providedover the carrier signal include secondary process variables, diagnosticinformation (including sensor diagnostics, device diagnostics, wiringdiagnostics, and process diagnostics), operating temperatures,temperature of the sensor, calibration information, device ID numbers,materials of construction, configuration or programming information,etc. Accordingly, a single hybrid field device may have a variety ofinput and output variables and may implement a variety of functions.

HART is an industry standard nonproprietary system. However, it isrelatively slow. Other companies in the industry have developedproprietary digital transmission schemes which are faster, but theseschemes are generally not used by or available to competitors.

More recently, a newer control protocol has been defined by theInstrument Society of America (ISA). The new protocol is generallyreferred to as Fieldbus, and is specifically referred to as SP50, whichis as acronym for Standards and Practice Subcommittee 50. The Fieldbusprotocol defines two subprotocols. An HI Fieldbus network transmits dataat a rate up to 31.25 kilobits per second and provides power to fielddevices coupled to the network. An H2 Fieldbus network transmits data ata rate up to 2.5 megabits per second, does not provide power to fielddevices connected to the network, and is provided with redundanttransmission media. Fieldbus is a nonproprietary open standard and isattracting attention in the industry.

As additional protocols and architecture gain popularity in theindustry, the industry will face greater and greater challenges meldingthese technologies together into a single distributed control system.For example, newer devices will be coupled to an existing distributedcontrol system. In these situations the signals coming from the controlroom may expect traditional analog or hybrid technologies, but the fielddevices may be coupled to an H1 or H2 Fieldbus network. Conversely, thecontrol room of the industrial plant may be renovated, with the inputsand outputs to the control room comprising a modem H1 or H2 field bus,and the individual signals running to some older analog and hybrid fielddevices, and newer Fieldbus based field devices.

In addition to the challenge of integrating various technologies into asingle distributed control system, newer field devices will havemaintenance modes and enhanced functions that are not accessible via anolder control system. In addition, even when all components of adistributed control system adhere to the same standard (such as theFieldbus standard), one manufacturer's control room equipment may not beable to access the secondary functions or secondary information providedby another manufacturer's field devices.

SUMMARY OF THE DISCLOSURE

The present invention provides an apparatus for providing wirelessaccess to field devices in a distributed control system having a controlroom that, for example, provides hard-wired access to the field devices,thereby allowing access to the field devices in the event of a failurethe hard-wired media.

In a first embodiment, each field device is provided with a wirelessport and a hardwired port and can be accessed from a control room by awireless handheld unit or a wireless terminal. In one configuration ofthis embodiment, the wireless port is powered by the control network towhich the field device is connected.

In a second embodiment, a field module having a wireless port isconnected to an existing control network. The field module providesaccess from a wireless handheld unit or a wireless terminal in thecontrol room to all field devices connected to the control network. Inone configuration of this embodiment, the field module is powered by thecontrol network to which it is connected.

In a third embodiment, an apparatus provides wireless communicationbetween multiple devices within a process control system, such asbetween field devices, control units, user terminals, controllers, etc.,using a wireless bus protocol. In one case, a process control system foruse within a process control environment includes a plurality of processcontrol field devices that operate within the process environment, and acontrol device adapted to receive a sense signal from or to provide acontrol signal to one or more of the plurality of process control fielddevices. First and second wireless transceivers are communicativelyconnected to different ones of the process control field devices and thecontrol device and communicate with one another using a bus protocol, tothereby provide wireless communications within the process controlsystem.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of a prior art distributed control system.

FIG. 2 is a diagram of industrial plant having two distributed controlsystems and shows three embodiments of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 is a block diagram of a prior art distributed control system(DCS) 10. DCS 10 is comprised of control room 12, controller 14,discrete/analog I/O unit 16, H2-to-H1 bridge 18, and a variety of fielddevices represented by solenoid 24, switches 26 and 54, valvepositioners 28, 46, and 52, transmitters 30, 34, and 44, processanalyzers 36 and 50. These devices represent any type of field deviceknown in the control art. Also shown in FIG. 1 are handheld units 38 and39, which are capable of accessing information in a hybrid orFieldbus-based field device via a physical wire connection, and a localoperator/user station 40, which is capable of communicating with fielddevice 30 over a physical wire connection.

Control room 12 includes computers, user I/O, various forms of datastorage devices, and other computing devices known in the art. Controlroom 12 is coupled to controller 14 via bus 20, which is typically aproprietary digital communications network or an open digitalcommunication network employing a proprietary protocol. Controller 14receives various commands from control room 12 and provides data tocontrol room 12.

As depicted in FIG. 1, DCS 10 is a hybrid system comprising twodifferent types of field devices. Devices 24-36 are traditional analog,discrete, and hybrid analog/digital devices, wherein the primary controlfunction of the device is realized by modulating a current. These fielddevices are coupled to discrete/analog I/O unit 16, with each deviceconnected to an individual channel of unit 16 by a single pair of wires(and possibly two additional power wires in the case of a traditionalfour-wire field device). For example, solenoid 24 is coupled viatwo-wire twisted pair 42 to channel 43 of unit 16.

For a traditional analog or discrete field device, the onlycommunication with the device occurs by modulating or switching thecurrent running through the two-wire twisted pair, with the magnitude ofthe current representing a measured process variable (as in the case ofthe transmitter), or an action requested by controller 14 (as in thecase of a valve positioner or solenoid). Traditional analog devices havea frequency response limited to approximately 10 Hz and receive powerfrom the two-wire twisted pair.

Hybrid analog/digital devices operate in a manner similar to traditionalanalog devices, but also allow digital communication of secondaryinformation by superimposing a digital carrier signal on the modulatedcurrent carried by the two-wire twisted pair. One such hybrid analogdigital system is known in the control art as Highway Addressable RemoteTransducer (HART) and transmits data in a manner similar to aconventional computer modem adhering to the Bell 202 specification.Generally, the primary function of these devices is still realized bymodulating the current through the loop, while other types of secondaryinformation, such as diagnostic data, operating temperature,identification codes, error codes, and secondary variables, aretransmitted digitally. In such a system, digital communication isrelatively slow and is limited to approximately 300 baud. When amaintenance person desires to test an analog device, the maintenanceperson must make a physical connection to the device itself, such aslocal operator/user station 40 connected to transmitter 30, or to thetwo-wire twisted pair leading to the device, such as handheld unit 38connected to the two-wire twisted pair leading to valve positioner 28.

In contrast, devices 44-54 are modem network-based digital fielddevices, wherein all information is digitally transmitted to and fromeach device. While many control system manufacturers have developedproprietary digital systems, the Standards and Practices Subcommittee 50of the Instrument Society of America has developed and specified anarchitecture known in the art as Fieldbus. The Fieldbus specificationincludes two types of networks, a lower speed network referred to as H1and a higher speed network referred to as H2. Both networks can supportmultiple connections to a single network bus, in contrast to traditionalanalog connections, which only support one device per two-wire twistedpair. While the present invention is described herein with reference toa Fieldbus network-based control system, in other embodiments thepresent invention may be employed in any distributed control systemhaving network-based field devices.

A Fieldbus H2 network can transmit data at a rate up to 2.5 megabits persecond. In addition, an H2 network includes two parallel sets ofphysical wire media: a primary wire media and a secondary, or redundant,wire media. Should the primary wire media fail, the secondary wire mediais automatically used by the DCS Because of the high capacity andredundancy of H2 Fieldbus networks, H2 Fieldbus networks are beginningto be used as a distribution network that connect the controller tovarious distribution units in the DCS. However, traditional distributionnetworks are proprietary networks using either parallel or serialcommunication.

In FIG. 1, H2 distribution network 22 couples controller 14 to H2-to-H1bridge 18, and proprietary bus 21 couples controller 14 todiscrete/analog I/O unit 16. In other configurations known in the art,unit 16 and bridge 18 may be coupled to a common distribution network.As previously discussed, discrete/analog I/O unit 16 includes discretechannels, with each channel coupled to a single device.

H2-to-H1 bridge links the data carried by proprietary distributionnetwork 22 to H1 Fieldbus control networks 45 and 47. H1 Fieldbuscontrol network 45 is coupled to transmitters 44, valve positioner 46,and relay 48, and H1 Fieldbus 47 is coupled to process analyzer 50,valve positioner 52, and solenoid 54. While an H1 Fieldbus network lacksredundant wiring, and has a lower data transmission rate ofapproximately 31.25 kilobits per second, it is capable of providingpower to the devices to which it is coupled, while an H2 Fieldbusnetwork does not. For the above reasons, the H1 Fieldbus network isideal for providing final connections to individual field devices, whilethe H2 Fieldbus network is ideal for distributing control signalsthroughout the physical plant controlled by the DCS.

More recently, field devices have been provided with microprocessors andadditional functionality. Such “smart” field devices are capable ofmonitoring a plurality of process variables, performing a variety ofcontrol functions, performing comprehensive diagnostics, and providing awide array of various types of status information. The Fieldbusspecification specifies a variety of primary functions that may besupported by various Fieldbus field devices. In addition, manymanufacturers have provided secondary functions beyond those specifiedin the Fieldbus specification. While Fieldbus field devices manufacturedby different manufacturers are compatible to the extent that onlyFieldbus specified functions are accessed, they are not compatible withrespect to the secondary functions. For example, a Fieldbus controllermanufactured by company A will generally not be able to access thesecondary functions provided by a Fieldbus valve positioner manufacturedby company B. Therefore, an industrial plant using a variety of Fieldbuscomponents provided by different manufacturers will not be able to useof all the functions provided by the various components.

The problem is worse in older distributed control systems that weredesigned to use traditional analog/discrete and hybrid devices. Often acompany will wish to preserve an investment in an existing installation,and will retrofit the installation with newer Fieldbus field devices. Insuch an installation, the control room will not even be able to accessthe standardized Fieldbus functions provided by the various devices.Accordingly, a need exists to access the secondary functions provided byvarious manufacturers, as well as standardized Fieldbus functions when aFieldbus based device is connected to an older distributed controlsystem.

The present invention is an apparatus and method for providing redundantwireless access to field devices in a distributed control system,thereby allowing access to field devices in the event of a failure ofthe hard-wired media that connects the field devices to a control room.The redundant wireless access can be used several ways. First, it can beused to allow continued operation of a distributed control system duringfailure or maintenance of the hard-wired media. However, even ifcontinued operation is not desired, redundant wireless access may stillbe valuable for monitoring process variables and performing controlactions, such as those required to shut down a process. For example,consider a distributed control system subjected to an explosion. Theexplosion, may render the hardwired media connecting field devices tothe control room inoperable. Using the redundant wireless accessprovided by the present invention, a control room operator will still beable to access field device to perform an orderly shut-down of thedistributed control system. The operator may observe criticaltemperatures and pressures, and adjust or close valves and other devicesto complete the shut down. By having redundant wireless access to thefield devices, the operator may be able to effect a shutdown in such away as to minimize losses.

FIG. 2 is a diagram of an industrial plant having two distributedcontrol systems. DCS 56 is comprised of control room 60 (which includesterminal 104 coupled to wireless link module 106, which in turn isconnected to wireless transceiver 108), controller 62, bus 64, fielddevice 66, valve positioner 68, transmitter 70, process analyzer 72, H1Fieldbus control network 74, transmitter 76, valve positioner 78,solenoid 80, field module 82, and H1 Fieldbus control network 84. DCS 58is comprised of control room 86 (which includes terminal 103 coupled towireless link module 107, which in turn is connected to wirelesstransceiver 109), controller 88, bus 90, H2 Fieldbus distributionnetwork 94, H2-to-H1 bridge 92, transmitters 96 and 100, valvepositioner 98, and H1 Fieldbus control network 102. Buses 64 and 90 arenormally proprietary digital communication networks, or opencommunication networks employing a proprietary protocol.

Two embodiments of the present invention are illustrated in DCS 56. Thefirst embodiment is illustrated by those field devices coupled to H1Fieldbus control network 74. Each field device on control network 74includes a wireless transceiver. Field device 66 represents any-genericfield device coupled to control network 74 and includes wirelesstransceiver 114. Valve positioner 68 includes wireless transceiver 116,transmitter 70 includes wireless transceiver 118, and process analyzer72 includes wireless transceiver 120. Each wireless transceiverimplements a redundant wireless Fieldbus connection with terminal 104,thereby allowing redundant wireless access to each field device fromcontrol room 60.

Another novel feature of the present invention is that the wirelessFieldbus port attached to each field device is powered by the hardwiredH1 Fieldbus port attached to each device. Since the wireless Fieldbuslink of the field devices is powered by the existing H1 Fieldbus controlnetwork, no additional wiring is required.

The wireless links disclosed herein represent any wireless communicationmethod known in the art, including, but not limited to, radio, infrared,visible light, and ultrasonic forms of wireless communication.

A second embodiment of the present invention is illustrated by thedevices connected to H1 Fieldbus control network 84. Transmitter 76,valve positioner 78, and solenoid 80 are each coupled to control network84. Also coupled to control network 84 is field module 82, whichincludes a wireless transceiver 122 powered by H1 Fieldbus controlnetwork 84. Field module 82, in essence, forms a wireless bridge betweencontrol network 84 and terminal 104 in control room 56, and allowsterminal 104 to access each device coupled to H1 Fieldbus controlnetwork 84. Accordingly, field module 82 is ideally suited for providingredundant wireless access in an existing environment having a variety ofH1 Fieldbus devices from different manufacturers.

A third embodiment of the present invention is illustrated by DCS 58. InDCS 58, controller 88 is coupled to H2-to-H1 bridge by H2 Fieldbusdistribution network 94. H2-to-H1 bridge links H2 Fieldbus distributionnetwork 94 to H1 Fieldbus control network 102. H2-to-H1 bridge alsoincludes a second Fieldbus port connected to wireless transceiver 124,and communicates with a remote device such as terminal 103. Accordingly,terminal 103 in control room 86 can access all field devices serviced bythe H2-to-H1 bridge, such as transmitters 96 and 100 and valvepositioner 98. In other configurations, it is common for an H2-to-H1bridge to service a plurality of H1 Fieldbus control networks, in whichcase all field devices connected to all control networks serviced by theH2-to-H1 bridge can be accessed remotely.

The present invention provides wireless redundant access to fielddevices in a distributed control system having a control room thatprovides hardwired access to the field devices. In a modem distributedcontrol system having Fieldbus devices coupled to a Fieldbus controlroom, the present invention provides a redundant wireless access to aterminal having a wireless link. The apparatus of the present inventionallows access to field devices in the event of failure or otherunavailability of the hard-wired media that couples the control room tofield devices.

In one embodiment, each Fieldbus-based device is provided with its ownsecondary wireless H1 or H2 Fieldbus port that is powered by the H1Fieldbus control network. This embodiment provides maximum flexibilitybecause no modification of the distributed control system is required,and is ideally suited for new devices that are to be added to anexisting Fieldbus installation. As soon as the H1 Fieldbus device isconnected to the existing H1 Fieldbus control network, the device can beaccessed via the wireless terminal.

In another embodiment of the invention, a field module is connected toan existing Fieldbus control network. The field module has a wireless H1or H2 Fieldbus port that is powered by the H1 Fieldbus control network,and provides access from the wireless terminal to all Fieldbus devicesconnected to the control network. This embodiment is ideally suited fordistributed control systems that already have Fieldbus devices.

In yet another embodiment of the present invention, the distributedcontrol system is provided with an H2-to-H1 bridge having one or more H1control networks coupled to Fieldbus devices, a hard-wired H2 portcoupled to a controller, and a wireless H2 or H1 Fieldbus port. Thewireless Fieldbus port allows a wireless terminal to access all Fieldbusdevices on all H1 control networks serviced by the H2-to-H1 bridge.

Although the present invention has been described with reference topreferred embodiments, workers skilled in the art will recognize thatchanges may be made in form and detail without departing from the spiritand scope of the invention.

1. A process control system for use within a process control environment, comprising: a process control field device; a control device for receiving a sense signal from or providing a control signal to the process control field device; a first wireless radio frequency transceiver communicatively connected to the process control field device; and a second wireless radio frequency transceiver communicatively connected to a second process control field device or to the control device; wherein the first wireless radio frequency transceiver communicates with the second wireless radio frequency transceiver using a bus protocol.
 2. The process control system of claim 1, wherein the bus protocol is a standard bus protocol.
 3. The process control system of claim 2, wherein the standard bus protocol is a fieldbus protocol.
 4. The process control system of claim 1, wherein the bus protocol is an open communication protocol.
 5. The process control system of claim 1, wherein the bus protocol is an SP50 communication protocol.
 6. The process control system of claim 1, wherein the bus protocol is a digital communication protocol.
 7. The process control system of claim 1, wherein the process control field device communicates with the control device via a hardwired communication path using the bus protocol.
 8. The process control system of claim 7, wherein the control device includes a user terminal and a controller.
 9. The process control system of claim 1, wherein the process control field device generates a sense signal indicative of a sensed parameter and a secondary signal and wherein the first wireless radio frequency transceiver communicates both the sense signal and the secondary signal.
 10. The process control system of claim 9, wherein the secondary signal is a status signal indicating a status the process control field device.
 11. The process control system of claim 10, wherein the status signal includes at least one of a diagnostic signal, an identity signal, and a calibration signal.
 12. The process control system of claim 1, wherein the process control field device comprises a member of the group consisting of a valve positioner, a flow transmitter, a temperature sensor and a pressure sensor.
 13. The process control system of claim 1, wherein the control device includes a user terminal.
 14. The process control system of claim 13, wherein the control device further includes a controller.
 15. A communication system for use in a process control system within a process control environment having a plurality of process control field devices that operate within the process control environment and a control unit for providing signals to or receiving signals from the plurality of process control field devices, the communication system comprising: a first wireless radio frequency transceiver communicatively connected to a first one of the plurality of process control field devices; and a second wireless radio frequency transceiver communicatively connected to a second one of the plurality of process control field devices or to the control unit; wherein the first wireless radio frequency transceiver communicates signals to or receives signals from the second wireless radio frequency transceiver using a bus protocol.
 16. The communication system of claim 15, wherein the bus protocol is a standard bus protocol.
 17. The communication system of claim 16, wherein the standard bus protocol is a fieldbus protocol.
 18. The communication system of claim 15, wherein the first wireless radio frequency transceiver communicates a sense signal indicative of a measured physical parameter to the second wireless transceiver using the bus protocol.
 19. The communication system of claim 15, wherein the first wireless transceiver receives a control signal to cause one of the plurality of field devices to perform a physical action within the process control environment from the second wireless transceiver using the bus protocol.
 20. The communication system of claim 15, wherein the first wireless radio frequency transceiver and the second wireless radio frequency transceiver communicate a secondary signal using the bus protocol.
 21. The communication system of claim 20, wherein the secondary signal is a status signal indicating a status of one of the process control field devices.
 22. A method of communicating within a process control environment having a plurality of process control field devices for sensing or altering parameters within the process control environment and a control unit for receiving a signal from or providing a signal to one or more of the plurality of process control field devices, the method comprising: connecting a first wireless radio frequency transceiver to a first one of the plurality of process control field devices; connecting a second wireless radio frequency transceiver to a second one of the plurality of process control field devices or to the control unit; and wirelessly communicating a radio frequency signal between the first wireless radio frequency transceiver and the second wireless radio frequency transceiver using a bus communication protocol.
 23. The method of communicating within a process control environment of claim 22, wherein wirelessly communicating a radio frequency signal between the first wireless radio frequency transceiver and the second wireless radio frequency transceiver includes using a standard bus communication protocol.
 24. The method of communicating within a process control environment of claim 23, wherein the standard bus communication protocol is a fieldbus protocol.
 25. The method of communicating within a process control environment of claim 22, wherein wirelessly communicating a radio frequency signal between the first wireless radio frequency transceiver and the second wireless radio frequency transceiver includes communicating a sense signal indicative of a sensed parameter.
 26. The method of communicating within a process control environment of claim 22, wherein wirelessly communicating a radio frequency signal between the first wireless radio frequency transceiver and the second wireless radio frequency transceiver includes communicating a control signal to cause a process control field device to perform a physical control action.
 27. The method of communicating within a process control environment of claim 22, wherein wirelessly communicating a radio frequency signal between the first wireless radio frequency transceiver and the second wireless radio frequency transceiver includes communicating a status signal.
 28. The method of communicating within a process control environment of claim 27, wherein the status signal includes at least one of a diagnostic signal, an identity signal, and a calibration signal. 